1. Field of the Invention
The invention relates to a superconducting cable which has a central superconducting electrical conductor, a dielectric which surrounds the same and a superconducting return conductor which is arranged above the same.
2. Description of Related Art
A cable such as this is disclosed in EP 0 830 694 B1.
In modern technology, a superconducting cable has electrical conductors composed of a composite material which contains ceramic material that changes to the superconducting state at sufficiently low temperatures. The electrical direct-current resistance of a correspondingly constructed conductor is zero, if the coolant is adequate, provided that a specific current level is not exceeded. By way of example, suitable ceramic materials are materials doped with rare earths, which have become known by the name ReBCO (rare-earth barium-copper oxide), in particular including YBCO (yttrium-barium-copper oxide). Another of these superconducting materials is, for example, BSCCO (bismuth-strontium-calcium-copper oxide). Sufficiently low temperatures to change a material such as this to the superconducting state are, for example, between 67 K and 110 K. Suitable coolants are, for example, nitrogen, helium, neon and hydrogen, or mixtures of these substances.
DE 197 24 618 A1 describes a superconductor which consists of a corrugated metal tube, which is welded with a longitudinal bead and has a superconducting layer based on ceramic materials. The wall of the superconductor consists of a metallic support on which a metal foil, to which the superconducting layer is fitted, is applied by means of an adhesion promoter.
The initial cited EP 0 830 694 B1 discloses a superconducting alternating-current cable having a forward conductor and a return conductor, which is arranged concentrically with respect thereto. Both conductors are in the form of conductor arrangements composed of a plurality of conductor layers. In order to produce the forward conductor, a plurality of layers of superconducting individual conductors are wound at predetermined angles around a cylindrical support. A dielectric of sufficient radial size is applied to the finished forward conductor, around which the return conductor is arranged, by winding on a plurality of layers of superconducting individual conductors. The production of this known cable is complex. With corresponding use of material, it has relatively large radial dimensions which also require a correspondingly large cryostat, in which the cable is arranged for operation as a superconducting cable, and through which the coolant is passed.